“Downsizing” and “function integration” are the recent trends in developing information appliances. For a multi-function peripheral (referred to as an MFP), integrating printer, copier, fax and scanner functions not only means the combination and reorganization in physical structures, but also the merging and simplification of the functional related components under the requirement of downsizing.
A printer usually uses a paper sensor and a media sensor to determine the categories and the sizes of paper. Since the scan module has better sensing granularity and the capability to distinguish the scanned results of the three primary colors (i.e., red, green and blue), the paper and media sensors are replaced by the scan module in MFPs. Although scan modules can be used to determine the sizes and the categories of paper by the optical characteristics of scan modules, how to precisely determine the sizes and the categories of paper is still an important issue since there are various types of printable media including plain paper, transparencies and photo-paper. Because printing parameters are adjusted according to the category of paper, the determination results will affect the quality of printing. In addition, since the used paper determination method affects the precision of the determination, the quality of the used paper determination method is the key of the quality of printing.
One prior paper determination method is to print invisible ink codes which indicate the paper categories, manufacturers and some attributes on the paper. The advantage of this method is its high precision in determination. However, since the codes become visible when covered by ink, they are usually printed on the borders of the paper. As a result, the codes are visible in a full-bleed printing mode, and hence, the paper determination method is still problematic.
Another paper category determination method is to detect the diffuse reflectance and specular reflectance of paper with two sensors. The reflectance ratio of these two values is then compared with that of other known media stored in a database to determine the categories of paper. However, the precision of this method is not good enough because there are several media with the same reflectance ratio. As a result, printing parameters cannot be adjusted correctly.
Another paper category determination method utilized in the products of Hewlett-Packard Company is to obtain the reflectance factors by optical scanning, process these factors by Fourier transforming, and compare the frequency magnitude of the transformed signals to that of known media. Although this determination method avoids the problems mentioned above, the precision of determination is still not good enough since the frequency magnitude of the unknown medium is sometimes similar to that of known media in the database. This results from the competition of market, because of which an increasing number of media categories are produced with similar properties, and hence, the difficulty and error rate of determination is increased.
In addition, scan modules are capable of detecting the three primary colors, and hence can be used in paper determination in MFPs.